Centrifugal compressor



R. BIRMANN G'ENTRIFUGAL COMPRESSOR Filed May 21, I942 zms zm 2 Sheets-Sheet 1 N INVENTOR.

ATTORNEYS .mdaw 217mm Hg. 6; 3%4. BIRMANN 2,4052

CENTRIFUGAL COMPRES SOR Filed May 21, 1942 2 Sheets-Shet 2 V INVENTOR. 1 B Q @1 ATTORNEYS Patented Aug. 6 1946 CENTRIFUGAL COIVIPRESSOR Rudolph Birmann, Newtown, Pa., assignor, by mesne assignments, to Federal Reserve Bank of Philadelphia, a cor States of America poration of the United Application May 21, 1942, Serial No.443,9 57 17 Claims. (Cl. 230-130) This invention relates to centrifugal compressors, and has particular reference to the construction and mounting of impellers therein.

The mounting of impellers operating at very high rotational speeds involves various difficulties, particularly in the case of mounting on a common shaft a plurality of impellers providing successive compressor stages. For example, when such impellers are directly driven at the speed of a gas turbine, they may operate substantially above the critical speeds for the rotating parts, and provision for flexibility is essential. Furthermore, provision must be made to take care of expansion, either due to temperature changes involved in the compression of air, or the heating up of the compressor by reason of its position adjacent to a combustion turbine, combustion chambers, internal combustion engines, or the like.

For high speed operation, and particularly in the case of aircraft construction where weight must be kept at a minimum, it is essential that the impellers should be made 'of light aluminum or magnesium alloys or th like, which inthemselves do not have sufiicient strength orrigidity to permit the complet elimination of all parts of steel construction. It is one object of the present invention to provide a compressor construction to avoid the difiiculties above mentioned and particularly to enable the assembly of light metallic impellers with shafts or aligning members of steel.

' The above and other objects of the invention, particularly relating to details, will becom apparent from the following description, read in conjunction with the accompanying drawings, in which:

Figure 1 is a fragmentary axial section through a multiple stage compressor embodying various features of the invention;

Figure 2 is a fragmentary transverse section taken on the plane indicated at 2-2 in Figure 1; and

Figure 3 is a section generally similar to Figure 1 but showing an alternative arrangement embodylng features of the invention designed particularly for the assembly of two adjacent impellers.

Referring first to the modification of Figures 1 and 2, there is indicated therein, in fragmentary form, a centrifugal compressor having four impellers 2, 4, 6 and 8, rotating together about a common axis and forming the successive impellers of four compressor stages. The type of compressor illustrated is particularly designed for an internal combustion power plant of the type described, for example, in my application Serial No.

2 439,569, filed April 18, 1942. As described in aid application, the impellers are designed to be directly driven by a turbine at very high rotary speeds. Each of the impellers is preferably of the type dsecribed in my application Serial No. 441,686,

filed May 4, 1942, though it will be obvious that the invention is applicabl to impellers of substantially different design. In accordance with the disclosure of the last named application, and also in accordance with my application Serial No. 407,408, filed August 19, 1941, each impeller is made in two parts, both to permit easier machin ing and to effect the damping of vibrations which may be set up in the impeller blading during operation. Accordingly, the impeller 2 comprises two sections Ill and I2. The outlet section ID of this impeller'is integral with the inlet section M of the next impeller 4, which is provided with a separate outlet section l6. Similarly, the impellers 6 and 8 are made of separat sections I8 and 20 in the one case and 22 and 24 in the other, the sections l8 and 22, namely, the outlet section of impeller 6 and the inlet section of impeller 8, being integral as illustrated. In order to hold the two sections of the impellers in angular alignment, the impeller sections are splined upon tubular members 26, 28 and 30. These tubular members may be conveniently referred to as shaft members, though it will be noted hereafter that, except for 28, they do not function as true shafts from the standpoint of taking care of lateral bending forces, having merely the function of aligning the respective impeller sections to which they are common and to transmit torque in addition to providing flanges to aid in securing the impeller sections together.

The construction involved in the case of all of the shaft members 26, 28 and 30 will be best understood from considering the section of Figure 2, which shows the impeller section 20 provided with internal teeth engaging the external teeth of the shaft section 28 as indicated at 32. These teeth are, to secure maximum strength, preferably of internal and external gear form of sub stantially the same pitch diameter so as to form a close fitting spline arrangement preventing any substantial relative rotation between the shaft member and any of the impeller sections to which it is splined. The various impeller sections carried by the shaft member 28 are connected in pairs [4, l6 and I8, 20 by means of bolts 34 and 35, the heads of which engage, and are sunk into countersinks in, flanges 36 and 38 carried by the shaft member 28. The bolts 34 and 35, of which 46 on the shaft members 20 and 26, respectively;

serve to hold together theimpeller. sections 10 and I: on the one hand and 22 and 24 onthe 7 other.

The mounting of the assembly which has been described comprises three bearings, the housings of which are indicated at 48, 50 and 54. The bearing 48 surrounds the central portion of the shaft member 28, the parts thereof being split for assembly about this member. The bearing within the housing 50 mounts the shaft member 25, while that within the housing 54 mounts a shaft extension 52 secured to the impeller section 24.

It will be evident from the foregoing description that a strong impeller assembly is provided, between the various separate parts of which torque is transmitted through the steel tubular shaft sections such as 26, 28 and 30, described above, avery strong construction being provided by the use of external and internal gear teeth having close sliding fits with each other. The various connecting bolts are relieved by the splining arrangement from the transmission of torque and serve solely to draw the various impeller sections together. These connecting bolts are threaded to an initial tension condition to provide an axial pressure between the impeller sections exceeding any tension forces that may exist between the separate sections ofeach impeller due to the lateral bending or deflection of the rotor, i. e., the boltshave the function of insuring that the impeller sections do not part from each other during operation. By u'ndercuttin the meeting ed es of the vanes, as described in said application Serial No. 407,408, referred to above, an elastic contact between the impeller vanes is secured.

In'the compressor construction illustrated in Figure 1, the stationary casing and the impellers are made of either the same aluminum or other light alloy, or of different alloys having substantially thev same c'oefllcients of expansion. It will be evident that if this is the case, except for the steel shaft members which have been described, the expansion characteristics of the casing and the rotor as a Whole should be substantially the same, so that clearances betweenv the rotor parts and'the stationary casing parts would remain substantially constant. This, it will be obvious, will be the effect of having the expansions of the various light alloy partsof the rotor measured from the flanges carried by the steelshaft members 26, 28 and 30. For example, it will be evident that if the flange 36'be considered as the origin for the expansion of the portions to the left thereof, the axial movement of the flange 42 will be essentially that resulting from the expansion of the impeller sections between these flanges. Likewise, this will be true in the 'case of the movement of the flange 46 with respect to the flange 38. It will be evident, therefore, that, except for the expansion of the short length of steel shaft between the flanges 36 and 38, the amount cf expansion'of" the rotor is measured solely by the expansion of the aluminum alloy parts thereof; and since the stationary casing has an expansion also measured by the expansion of the alloy involved in its construction, the clearances all along the shaft remain substantially constant, the spacing between the flanges 36 and 38 being insufficient to disturb to any substantial degree this correspondence of expansibility at all points along the axis.

In the case of the modification of Figure 3,

there is involved an alternative construction embodying some of the same general principles involved in the previousmodification. In the case of this modification, there are shown two impellers '55 and 58, which may be used as the sole two stages of a compressor, or may form a pair of stages of, for example, a four-stage compressor of the type illustrated in Figure l, in which case their shaft would be continued on the other side of a central bearing. The impeller 56 comprises the two sections 6!] and 52, while the impeller 58 comprises the two sections 54 and 66. In each instance, one of these sections is undercut in accordance with the disclosures of said applications Serial Nos. 407,408 and 441,686, referred to above. Between the impeller sections 6 3 and 66 is a separating member 68, which has the surface thereof formed to cooperate with a fixed member E0 to provide labyrinthine packing between the stages. The sections 68 and 62 are held in angular alignment by means of a series of bushings spaced about the axis, one of which bushings is indicated at 12, these bushings being driven into aligned openings in the adjacent faces of the impeller sections. Similar bushings M hold in angular alignment the impeller sections 64 and 66. The angular alignment of the impeller sections so maintained are, of course, suchas to cause the impeller vane surfaces to be substantially smoothly continuous from one section to the other.

A steel shaft i6 is splined at 18 to the various impeller sections and to the intermediate member 58, this splining being the same as that involved in the previous modification and illustrated speoifically in Figure 2. This splining, as before,

serves to transmit torque to the various impeller sections and so substantially relieves the bushings I2 of torque transmission, the spline teeth. being in accurate alignment when the bushings are in place.

Threaded on the right hand end of the shaft 16 is a ring 80, which is turned to a position such that rods 82, having close fit within the bushings l2 and M and extending through aligned openings in the various'impeller sections and. the member 68, may be threaded thereinto. The left hand ends of these rods are provided with nuts 84 which are located in countersinks in. the impeller section 62 and are tightened to draw the various rotor parts together to the necessary degree.

The shaft 16 is mounted in bearings within the housings 86 and 88, respectively.

In the modification just described, the, rods 82 are desirably formed of the same material as the stationary casing, for example of magnesium alloy. Under such conditions, if the bearing 88 is a thrust bearing (for example, of the type disclosed in my application Serial No. 408,787, filed August 28, 1941), it will represent the fixed origin for the expansion of both the rotor and the casing. Since it .is adjacent the threaded ringv 80, it will be evident that the movement of the nut 84 with respect thereto will be substantially completely defined by the expansion of the magnesium' alloy rod 82 and will correspond to the movement of the portions'of the casing having the same position. along the axi as the nut 84. Thus the various stationary and rotary parts are so maintained that the clearances remain essentially constant, this being particularly true in view of the fact that the aluminum .alloy impeller parts will also have a coeffiicent' of expansion less than, but approximately that of the magnesium alloy rods 82. The spacer 68 is preferably of magnesium alloy to get a maximum expansion throughout its length. As expansion takes place, the pressure gradient across the impeller assembly will cause the impeller sections to slide to the left along the shaft in the same direction as the casing expands, imposing tension on the rods 82.

As an alternative to the arrangement of Figure 3, but functioning in the same fashion, a tubular expansion member made from magnesium alloy may extend lengthwise within the hollow shaft, being locked to the shaft at one end at or near the thrust bearing, with its other end arranged to take the axial thrust of the sildeable rotor elements, i. e., the impellers and spacers. In such case, for example, the inlet face of the impeller section 62 would be connected to the expansion tube by means of pins or keys extending inwardly from the impeller section through slots in the shaft into the tubular expansion member.- Such arrangement has the advantage of avoiding the necessity for having any openings extend through the impeller hubs.

What I claim and desire to protect by Letters Patent is:

l. A compressor comprising'a casing, a bearing within the casing, a shaft member mounted in said bearing, a rotor comprising at least one impeller splined to said shaft member, said rotor and shaft member having substantially different coefficients of thermal expansion, and a plurality of rods, each of the rods being secured to the shaft member at a location on the high pressure side of the impeller, extending to the low pressure side of the impeller, and at the latter side engaging the rotor to limit axial movement of said rotor relative to the shaft member.

2. A compressor comprising a casing, a bearing within the casing, a shaft member mounted in said bearing, a rotor comprising at least one impeller mounted on said shaft member, and a plurality of rods, each of the rods being secured to the shaft member at a location on the high pressure side of theimpeller, extending to the low pressure side of the impeller, and at the latter side engaging the rotor to limit axial movement of said rotor relative to the shaft member, each of said rods having a coefficient of thermal expansion approximately the same as that of said casing.

3. A compressor comprising a casing, a hearing within the casing, a shaft member mounted in said bearing, a rotor mounted on said shaft member, and a plurality of elongated axially-extending members, one end of each of said elongated members engaging said shaft member at a location adjacent said bearing and at its opposite end engaging said rotor to limit axial movement of the rotor relative to the shaft member, each of said elongated membershaving a coefficient of thermal expansion approximately the same as that of said casing.

4. A compressor comprising a casing, a bearin within the casing, a shaft member mounted. in said bearing, a rotor mounted on said shaft member, and a pluralityof elongated axially-extending members, one end of each of said elongated members engaging said shaft member at a location adjacent said bearing and at its opposite end engaging said rotor to limit axial movement of the rotor relative to the shaft member, said rotor having a coefficient of thermal expansion approximately the same as that of said casing.

5. A compressor comprising a casing, a hearing within the casing, a shaft member mounted in said bearing, a rotor splined to said shaft member, said rotor and shaft member having substantially different coefficients of thermal expansion, and axially extending means secured to the shaft member at a single axial location adjacent said bearing and engaging the rotor at a substantial distance from the bearing to limit axial movement of said rotor relative to the shaft member.

6. A compressor comprising a casing, a bearing within the casing, a shaft member mounted in said bearing, a rotor mounted on said shaft member, said rotor and shaft member having substantially different coefficients of thermal expansion, and axially extending means secured to the shaft member at a single axial location adjacent said bearing and engaging the rotor at a substantial distance from the bearing to limit axial movement of said rotor relative to the shaft member.

-7. A compressor comprising a casing, a bearing within the casing, a shaft member mounted in said bearing, a rotor splined to said shaft member, said rotor and shaft member having substantially different coefficients of thermal expansion, and a plurality of axially extending rods distributed about the axis of rotation, each of said rods being secured at one end to the shaft member at a single axial location adjacent said bearing and at its opposite end engaging said rotor under tension to limit axial movement of said rotor relative to the shaft member.

8. A compressor comprising a casing, a hearing within the casing, a shaft member mounted in said bearing, a rotor mounted on said shaft member, said rotor and shaft member having substantially different coefficients of thermal expansion, and a plurality of axially extending rods distributed about the axis of rotation, each of said rods being secured at one end to the shaft member at a single axial location adjacent said bearing and at its opposite end engaging said rotor under tension to limit axial movement of said rotor relative to the shaft member.

9. A compressor comprising a casin a hearing within the casing, a shaft member mounted in said bearing, a rotor mounted on said shaft member, said rotor and shaft member having substantially different coefficients of thermal expansion, and a plurality of axially extending rods distributed about the axis of rotation, each of said rods being secured at one end to the shaft member at a single axial location adjacent said bearing and at its opposite end engaging said rotor to limit axial movement of said rotorrelative to the shaft member.

10. A compressor comprising a casing, a bearing Within the casing, a shaft member mounted in said bearing, a rotor comprising a plurality of impeller sections mounted on said shaft member, and a plurality of axially extending rods distributed about the axis of rotation, each of said rods being secured at one end to the shaft member at a single axial location adjacent said bearing, extending through an impeller section adjacent said bearing, and at its opposite end engaging an impeller section more remote from the bearing to limit axial. movementof the impellersections relative to the shaft member. 7 L.

11. A compressor comprising a casing, a bearing within the casing-a shaft member mounted in said beraing, a rotor comprisinga plurality of impeller sections mounted. on saidshaft memher, and a plurality of axially extending rods distributed about the axis of rotation, each of said rods being secured at one end to the. shaft member at a single axial. location adjacent said bearing, extending through an impeller section adjacent said bearing, and at its opposite end engaging an impeller section more remote from the bearing under tension to limit axial movement of the impeller sections relative to the shaft member. j

12. A compressor comprising a casing,. a bear--v ing within the casing, a shaftmember mounted in said bearing, a rotor, comprising a plurality of impeller sections, mounted on said shaft member, and .a: plurality of axially extending rods distributed about-the axis of rotation, each of, said rods being secured at one end on the high pressure side of the impeller to the shaft member at a single axial location adjacent said bear ing, extending through an impeller section adjacent said bearing towards the low pressure side of the impeller, and at its opposite end engaging an impeller section more remote from the bearing to limit axial movement of the impeller sections relative to the shaft member.

13. A compressor comprising a casing, a bearing within the casing, a shaft member mounted in said bearing, a rotor splined to said shaft member, said rotor and shaft member having substantially different coefficients of thermal expansion, and axially extending means secured to the shaft member at a single axial location adjacent said bearing and engaging the rotor at a substantial distance from the bearing to limit axial movement of said rotor relative to the shaft member, said axially extendingmeans having 'a coeflicient of thermal expansion approximately the same as that of the casing.

14. A compressor comprising a casing,a pair of spaced bearings within the casing, a pair of shaft members mounted in said bearings, and a multi-part rotor, said rotor comprising two parts respectively mounted on the shafts adjacent the bearings and another part mounted on both shafts, and bridging a spacebetween them, and means extending axially past thefirst mentioned parts connecting the last mentioned parts to the respective shafts at points adjacent the bearings.

15. A compressor comprising a casing, a'pair of spaced bearings within the casing, a pair of shaft members mounted in said bearings and spaced from each other, and a rotor secured to said shaft members only adjacent said-bearings and bridging the space between them, said rotor having a coefficient of thermal expansion substantially different from that of said shaft mem-. bers.

16. A compressor comprising a casing, a pair of spaced bearings within the casing, a pair of shaft members mounted in said bearings and spaced from each other, and a rotor splined to each of, said shaft members, secured to said shaft members only adjacent said bearings and bridging the space between them, said rotor having a coefiicient of thermal expansion substantially different from that of said shaft members.

1'7. A compressor comprising a casing, a'pair of spaced bearings within the casing, a pair of shaft members mounted in said bearings and spaced from each other, and a rotor secured to said shaft members only adjacent said bearings and bridging the space between them, said rotor having a coefficient of thermal expansion substantially different from'that of said shaft members, and approximately the same as that of said casing.

RUDOLPH BIRMANN. 

